(Meth)acrylic acid is generally prepared by gas phase oxidation of propane, propylene, (meth)acrolein, and the like in the presence of a catalyst. For example, propane, propylene, and the like are converted to (meth)acrylic acid through (meth)acrolein by gas phase oxidation in the presence of an appropriate catalyst in a reactor, and a reaction product mixed gas including (meth)acrylic acid, non-reacted propane or propylene, (meth)acrolein, an inert gas, carbon dioxide, water vapor, and various organic by-products (acetic acid, heavies, and the like) is obtained in the back end of the reactor.
The (meth)acrylic acid-containing mixed gas contacts with an absorption solvent including water in a (meth)acrylic acid absorption tower, and is recovered as a (meth)acrylic acid aqueous solution. Further, a (meth)acrylic acid-stripped insoluble gas is recycled for a synthesis reaction of (meth)acrylic acid, and a part thereof is incinerated, converted into harmless gas, and discharged. The (meth)acrylic acid aqueous solution is extracted, distilled, and purified to obtain (meth)acrylic acid.
Meanwhile, various methods of controlling process conditions or a process sequence and the like to improve the recovery efficiency of (meth)acrylic acid have been suggested. Among them, a method is known wherein a part of the (meth)acrylic acid aqueous solution obtained in a (meth)acrylic acid absorption tower is fed to an extraction tower, a (meth)acrylic acid extract with reduced water content and the raffinate are obtained using a hydrophobic solvent, and the extract and the residue that is not fed to the extraction tower, among the (meth)acrylic acid aqueous solution obtained in the absorption tower, are distilled together.
Further, a method for reducing energy consumption is known, by selectively discharging an aqueous solution including (meth)acrylic acid of a low concentration at the middle stage of the absorption tower to obtain a high concentration (meth)acrylic acid aqueous solution at the lower part of the absorption tower, feeding the low concentration (meth)acrylic acid aqueous solution discharged at the middle stage of the absorption tower to the extraction tower, obtaining a (meth)acrylic acid extract with reduced water content and the raffinate using a hydrophobic solvent, and feeding the high concentration (meth)acrylic acid aqueous solution and the (meth)acrylic acid extract to the distillation tower and conducting azeotropic distillation.
However, according to the known method of continuous recovery of (meth)acrylic acid, if the amount of the hydrophobic solvent in the extraction tower is increased so as to increase the (meth)acrylic acid extraction rate, the amount of the azeotropic solvent subsequently fed to the feed stage of the water separation tower may increase, the amount of the solvent fed to the water separation tower should be constantly maintained for the azeotropic distillation of water and solvent so that the content of (meth)acrylic acid in the upper discharge liquid of the water separation tower may be low, and thus the amount of the solvent introduced into the water separation tower as reflux may decrease, and a change in gas/liquid behavior in the water separation tower may be generated. Thus, as the upper tray of the water separation tower is dried, the separation efficiency of the water separation tower may decrease, and (meth)acrylic acid recovery rate may decrease.